Geochemistry and Mineralogy of Fresh and Altered Basalts from the Galapagos Rift

Schrader, Ed L.; Stow, Stephen H.

doi:10.2973/dsdp.proc.70.123.1983

Cited by 2 publications

(2 citation statements)

References 12 publications

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“…The presented dataset was supplemented by previously published magmatic sulphide data from Brothers volcano (n = 128; Keith et al 2017) and from mid-ocean ridges of the Atlantic (Kanehira et al 1973;MacLean 1977;Mathez 1980;Petersen 1984;Patten et al 2012Patten et al , 2013Marchesi et al 2013), Pacific (Mathez and Yeats 1976;Foder et al 1980;Distler et al 1983;Schrader and Stow 1983;Francis 1990;Ackermand et al 2007;Patten et al 2012) and Indian Ocean (Francis 1990;Yang et al 2014). …”

Section: Electron Probe Microanalysismentioning

confidence: 99%

Constraints on the source of Cu in a submarine magmatic-hydrothermal system, Brothers volcano, Kermadec island arc

Keith

Haase

Klemd

et al. 2018

Contrib Mineral Petrol

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Most magmatic-hydrothermal Cu deposits are genetically linked to arc magmas. However, most continental or oceanic arc magmas are barren, and hence new methods have to be developed to distinguish between barren and mineralised arc systems. Source composition, melting conditions, the timing of S saturation and an initial chalcophile element-enrichment represent important parameters that control the potential of a subduction setting to host an economically valuable deposit. Brothers volcano in the Kermadec island arc is one of the best-studied examples of arc-related submarine magmatic-hydrothermal activity. This study, for the first time, compares the chemical and mineralogical composition of the Brothers seafloor massive sulphides and the associated dacitic to rhyolitic lavas that host the hydrothermal system. Incompatible trace element ratios, such as La/Sm and Ce/Pb, indicate that the basaltic melts from L'Esperance volcano may represent a parental analogue to the more evolved Brothers lavas. Copper-rich magmatic sulphides (Cu > 2 wt%) identified in fresh volcanic glass and phenocryst phases, such as clinopyroxene, plagioclase and Fe-Ti oxide suggest that the surrounding lavas that host the Brothers hydrothermal system represent a potential Cu source for the sulphide ores at the seafloor. Thermodynamic calculations reveal that the Brothers melts reached volatile saturation during their evolution. Melt inclusion data and the occurrence of sulphides along vesicle margins indicate that an exsolving volatile phase extracted Cu from the silicate melt and probably contributed it to the overlying hydrothermal system. Hence, the formation of the Cu-rich seafloor massive sulphides (up to 35.6 wt%) is probably due to the contribution of Cu from a bimodal source including wall rock leaching and magmatic degassing, in a mineralisation style that is hybrid between Cyprus-type volcanic-hosted massive sulphide and subaerial epithermal-porphyry deposits.

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Section: Electron Probe Microanalysismentioning

confidence: 99%

Constraints on the source of Cu in a submarine magmatic-hydrothermal system, Brothers volcano, Kermadec island arc

Keith

Haase

Klemd

et al. 2018

Contrib Mineral Petrol

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“…Pyroxenes from the dike (Unit 39) exhibit peculiar plumose endings. Such a morphology, associated with a tendency for the plagioclase to form spherulitic aggregates, is characteristic of doleritic dikes and coarse-grained variolitic basalts (MacKenzie et al, 1982;Schrader and Stow, 1983).…”

Section: Pyroxenesmentioning

confidence: 99%

Mineral chemistry of volcanic sequences from Hole 917A, southeast Greenland Margin

Demant¹

1998

Proceedings of the Ocean Drilling Program

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During Ocean Drilling Program Leg 152, a 779-m-thick volcanic sequence was drilled at Hole 917A, on the feather edge of the seaward-dipping reflector sequence. The volcanic succession, which erupted under subaerial conditions, was subdivided into three series (Upper, Middle, and Lower) and 92 flow units. The Upper Series comprises picrites and olivine-phyric basalts. The Middle Series basalts are more evolved, and dacitic lavas and tuffs were erupted at the base of this series. Lavas from the Lower Series show a wider compositional range. A detailed mineralogical study of the different petrographical types shows that olivine is the principal phenocryst phase in the basalts, whereas clinopyroxene and plagioclase are the main components of the groundmass. High-Mg olivines (up to Fo 92.4 ) with chrome-spinel inclusions are abundant in the picrites and olivine-phyric basalts. Fo-content of the olivine decreases as a function of the composition of the whole rock except in some aphyric basalts with ophitic textures where the olivine underwent further re-equilibration during cooling. Plagioclase exhibits a large compositional range from bytownite (An 91 ) in the more primitive basalts to oligoclase (An 21 ) for the late crystallizing feldspar in the ophitic textures. Plagioclases from the Upper Series lavas are very poor in K 2 O. The presence of bytownite phenocrysts (An 86− 66 ) associated with sodic sieve-textured plagioclase (An 36−26 ) in the dacite (Unit 54) clearly demonstrates that this lava is a mixed lava. Pyroxenes are mainly clinopyroxene, but pigeonite and orthopyroxene were found in the matrix of some differentiated basalts with ophitic textures. The low Ti contents of the pyroxenes and the evolution trends are typical of tholeiitic lavas. The development of sector zoning in pyroxene microphenocrysts of the more differentiated basalts has a scattering effect on the distribution of the points on the pyroxene quadrilateral. Opaque oxides crystallize late and are mainly titanomagnetite. Ilmenite is also present in some lavas.The volcanic succession drilled at Hole 917A presents many petrographical and mineralogical similarities to the flood basalts of the Scoresby Sund region in East Greenland. These thick basaltic sequences, which characterize the North Atlantic volcanic rifted margins, were emplaced during a short time interval during the phase of continental breakup. The Lower and Middle Series have evolved in crustal magma chambers. The frequency of picrites in the Upper Series emphasizes an easier access of more primitive magmas to the surface during the final phase of rifting.

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Geochemistry and Mineralogy of Fresh and Altered Basalts from the Galapagos Rift

Cited by 2 publications

References 12 publications

Constraints on the source of Cu in a submarine magmatic-hydrothermal system, Brothers volcano, Kermadec island arc

Constraints on the source of Cu in a submarine magmatic-hydrothermal system, Brothers volcano, Kermadec island arc

Mineral chemistry of volcanic sequences from Hole 917A, southeast Greenland Margin

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